1. Field of the Invention
The present invention relates to a diagnosis apparatus for an internal combustion engine which detects abnormality of a linear air-fuel ratio (A/F) sensor for detecting an A/F of exhaust gas of the engine.
2. Description of the Related Art
An exhaust system in which a catalyst is provided at the exhaust pipe of the engine, and an A/F sensor for detecting components of the exhaust gas is attached on each of the upstream and downstream sides of the catalyst, whereby an amount of fuel is corrected based on the detected values of these sensors thereby to efficiently purify the exhaust gas by the catalyst, is known. Since the efficiency of the exhaust system depends on the purification efficiency of the catalyst and the efficiencies of the A/F sensors, there is provided with a diagnosis apparatus for monitoring these efficiencies.
Thus, an example of the method for diagnosing the A/F sensor on the upstream side of the catalyst is proposed, for example, by JP-A-8-220051, in which the response time of the upstream-side A/F sensor is monitored at the time of forcedly changing the A/F.